1. Technical Field
The present invention relates to a poppet valve for controlling pressure in a fluid power assist steering system. In particular, the present invention relates to a method of making such a poppet valve.
2. Description of the Prior Art
A known fluid power assist steering system includes a pump for pumping hydraulic fluid under pressure to a fluid power assist steering gear. The output pressure demands on the pump can vary with the pump flow and system load restriction. This pressure must be limited to a predetermined maximum in order to protect the pump and other system components from damage. To this end, the pump contains a relief valve assembly.
The relief valve assembly includes a movable spring biased spool that contains an internal poppet valve assembly. The spool normally covers a fluid exhaust port. The spool is exposed to the output pressure of the pump. Output pressure is also communicated through an orifice to the opposite side of the spool, which contains a venting passage normally blocked by the poppet valve assembly. When the output pressure of the pump exceeds the predetermined maximum amount, the poppet valve assembly opens to exhaust fluid through the vent passage. The reduced pressure on this side of the spool allows the spool to move, opening the exhaust port, and thereby relieving the output pressure.
The prior art poppet valve assembly includes a poppet spring that biases a poppet against a poppet seat. The force applied by the poppet spring determines the pressure at which the poppet valve assembly opens. This force is determined by assembling the poppet valve assembly using shims to set the initial position of the poppet valve seat and, thus, the force applied by the poppet valve spring. Determining the correct number of shims to use in a particular poppet valve assembly is a time-consuming and labor-intensive process.